Right? Recasts are pretty much unique to daytime. However, I remember a few recasts on primetime shows. Seinfeld's father was a different actor in season 1 in the very beginning. Also with children, I guess, it's easier. On Mad Men they recast Don Draper's son.
The show (Peyton Place) had originally been envisioned as an anthology series about the various citizens of the town. Irna Phillips thought that it should have been a serial and persuaded Paul Monash as much.
It also helped that the writing seemed tailored for each of the actresses playing Gina. For example,I can't picture Robin Mattson playing the material Linda Gibboney played as Gina and vice versa. No way could I see Linda's Gina with Keith.